Cob/hay bale homes.

Hi there,

My husband and I are planning on having a homestead in the future. We are interested in building a kind of hay bale/cob hybrid home and I have a few questions and I thought, perhaps someone in this forum could answer them for me.

First, I should give a little background, we live in ontario and are planning on purchasing our land either in eastern or southern ontario. Due to the frigid temperature, and the troubles I have read about (http://small-scale.net/yearofmud/) as well as my background in home retrofits geared to efficiency, I realize that it is nearly impossible to build a purely cob building in this climate.

So I thought why not insulate with hay and still take advantage of the sculptural aspect as well as thermal mass that cob can offer us. I have read about bale cob construction but I do not believe that it would give us a high enough R-value for our climate.

Here is the idea, I would create a two layer wall, straw bale on the outside and cob on the inside, my roof would be a shed type. I plan on having 4 posts to support the roof (they would be separate from the structure of the actual house and stand near the end of our roofs overhang). Also, I plan on making a drop ceiling on the inside of the house in order to insulate with more hay. My floors will not be earthen, I plan on having tamped gravel, a vapor barrier more hay between floor joists and some kind of wood floors.

So my question to you fine folks is - firstly, is this a feasible idea? Secondly, would my bales need tensioning even though they will not be load baring? Is wrapping the vapor barrier up and over the foundation (probably made of urbanite) a good idea or will it make it difficult to tie into the walls? is urbanite an okay material for haybale construction, if so how would they tie together?

Thank-you for your time!
I'm excited to hear your ideas and advice.
-Melly

melly wrote:

So my question to you fine folks is - firstly, is this a feasible idea?

Feasible, I suppose... but not necessarily a good idea.  One of the important things to remember is that bale walls need to breathe.  In climates that go from cold to hot and back, and humid as I would guess southern Ontario to be, there is moisture going in and out with the seasons.  What will inevitably happen is that you will collect moisture on the cob wall next to the bales, and rot the structure from the inside out.  Dewpoints are a bitch.  I'm sure there's a solution, but you'll want to read up on how moisture moves in walls (even in conventional construction).

melly wrote:Secondly, would my bales need tensioning even though they will not be load baring?

If you have a dropped ceiling, your walls will have to carry that much load, anyway.  Otherwise, I'm not sure what you mean by that.

melly wrote:Is wrapping the vapor barrier up and over the foundation (probably made of urbanite) a good idea or will it make it difficult to tie into the walls?

Sounds like a really good way to pool water where you don't want it... so no.  And I don't think I'd use hay/straw for insulating a floor.

melly wrote:is urbanite an okay material for haybale construction, if so how would they tie together?

I first thought, hey, there's a good use for city people -- building material!  But wouldn't they stink after a bit?    But I guess it's someone's clever name for concrete rubble? 

I don't see why it would be any different than a new concrete footer.

if the drainage trench was dug a significant amount deeper than the floor, do you believe water would still pool there? if hay is not a good way to insulate the floor, would you recommend anything else that is natural? or would it be smarter for me to go with a modern insulation?

Do you think if I used a stucco sealant on the inside of the bale walls that would eliminate the moisture issues?

If my drop cieling was tied into the roof line, it would put the stress and weight of the house on the exterior posts - is what i was thinking. and I was talking about using a pretensioned wire system for the bales, unless a timber structure would be smarter.


Thank-you for your reply and baring with me, as i am slowly trying to retain the knowledge i would need in order to tackle a project of this size and importance.

I just wanted to add another note saying I found this comment on the greenbuildingadvisor.com forum:

I helped build a small 4 season hybrid cob/strawbale one room building with a rocket stove in Wisconsin. A structural stray bale wall was coated on the interior and exterior with a 2-3" layer of cob. It was a pleasure to build and the cob application to a straw bale wall worked well to lock everything together and fill in the gaps. I think the walls ended up with decent insulation value and are likely sufficiently air tight with good hygrothermal properties. ~2' overhangs are meant to keep the rainwater off the exterior walls so the exterior wall finish can remain cob.
The thermal weakness of the overall design was the roof and wall to roof transition. The designer/builder had collected 3" ironwood trunks from the site and assembled a roof structure in place from this material. The organic form made it difficult to insulate, air seal and the rainwater management is questionable.

melly wrote:
if the drainage trench was dug a significant amount deeper than the floor, do you believe water would still pool there?

What drainage trench, and where?  You didn't mention anything of the sort.

melly wrote:
if hay is not a good way to insulate the floor, would you recommend anything else that is natural? or would it be smarter for me to go with a modern insulation?

Foam.

melly wrote:
Do you think if I used a stucco sealant on the inside of the bale walls that would eliminate the moisture issues?

No.

melly wrote:
If my drop cieling was tied into the roof line, it would put the stress and weight of the house on the exterior posts -

If you could design such a thing to meet your local codes for snow load, wind load, and dead load, I'd be impressed.  If, say, your wind load is 90mph, you've got a job on your hands.

Even if you're rural and not governed by the codes, it's a damn good idea to build it that way anyhow, for two reasons: one, those are guidelines for what sort of structural strength you need to survive in your climate.  And two, if the codes catch up to your area, which they inevitably do, you won't be able to sell the place if you don't build it to the standards. (Safe dwellings... one of the downsides of living in a civilized country....  )

Here in the US, you can build anything an engineer will put his stamp on.  Because that makes the engineer liable, however, there aren't many who undertake much in the way of unconventional building.

"if the drainage trench was dug a significant amount deeper than the floor, do you believe water would still pool there?"

where ever you build the drainage trench, it needs to run (downhill) to daylight or to a dry well, you don't want the water to collect at the bottom of the trench,no matter how deep it is.

"Do you think if I used a stucco sealant on the inside of the bale walls that would eliminate the moisture issues?"

you can use an earthen plaster of some kind, but not a cementious stucco.  There is a whole body of knowledge on the "sealing" of adobe and cob buildings.  It doesn't work.  The whole thing needs to breathe.  Seems like the cob and straw bales are a good pairing if you get the engineering right, and don't put sealants and vapor barriers in the way.  An engineer friend of mine says:  "you can never keep moisture completely out of anything, so don't try to seal it all up.  That just keeps it from drying out.  It's the water that gets trapped inside that causes the problems"

don't get discouraged, you'll figure it all out.  There is a lot to think about.

We are building a cob home....cob studio.

We first had to dig 5 feet trench down into pure clay. Our frost line was at 4 feet, at 5 feet we laid the French drain, covered it with drainage rock 3/4" (tampered), laid HUGE rocks and boulders on the exterior(stonewall) and we are currently laying 3 feet of cob walls on top of that.

We have started to install a trombe wall on our south wall. Our north wall is solid cob...we are also making plans to install a Rocket Stove just a foot below our floor. Our floor insulation is going to be slip straw....covered with planks of wood. The interior wall will be insulated up to the cob...we are hoping with the Rocket Stove to have it wrap around the interior wall (it will be surrounded/protected with clay and sand). Since cob is load bearing we only require support for our door. Our roof is going to be steel with wool as the insulator...and of course the roof will over extend the 2 ft. I do not think I mentioned the drywell that we also installed. That will be used for drainage...our drywall we handdug 7 ft down and had the French drain dump out into it at 5 feet. We have yet to get a sump pump for it, but it is not quite needed at this point.
Check out our website...we recently put the cob studio into it's own separate category...look for the tab labelled Cob Studio.
www.billygoatsgruff.org

You can find lots of books on Cob and Straw bale building at  http://www.grannysstore.com

You can get the book on Straw Bale Houses by Bill & Athena Steen in the library. It will give you lots and lots of info, including some mention of work that has been done in Canada. (including straw bales being used as floor insulation. However, if groundwater levels might be an issue that seems unwise.)

One thing you might consider, if you want the walls to be truly just infill and nonload bearing, is to go with a pole building plan. Less foundation cost to worry about as there isn't any to speak of.  Not much site preparation either. Insulation of the floors and plumbing becomes a bit more of an issue, but with normal care as to site selection, drainage is generally much less of a concern, as water has no way to get into the house. It's supposedly the cheapest way to build  as foundations take such a huge percentage of the cost of building.

You might consider a sort of pole building with a sort of giant wraparound deck and that way you can still get the straw bale and cob house you want..I would be a bit concerned about straight cob walls (the weight) but straw is light so the amount of clay needed to seal it  shouldn't be a problem  if planned for.

By the way, you want STRAW,  NOT hay. Straw tends to be almost entirely tubes of dry stem which will trap air,(especially when sealed with a clay slip).  Hay is heavier because it has a large percentage of leaf AND usually the stems are crushed or cracked to facilitate drying so the behaviour in terms of insulation properties between the two are very very different. 

you may also go to "HEMPHOUSE" on YouTube  http://youtu.be/il7yw0JFs5c
... and  instead of using Hemp.... you use various materials you can make with your Woodchipper
good luck !